Japetus' surface composition (organic material?!?)

Caption NASA originale:"These two color composite images of Saturn's moon Japetus from Cassini's visual and infrared mapping spectrometer were obtained on Dec. 31, 2004, an hour and a half before the New Year, at a distance of 121.000 Km (75.186 miles), with a spatial resolution of about 60 Km (37 miles).
The three colors used in the left mosaic correspond to 1.01, 1.51, and 2 microns, while the right mosaic is comprised of images at 3.0, 3.21, and 4.60 microns. The two images show the vast difference in the composition of the bright and dark regions of Japetus. As one moves from the near infrared 1 to 2 micron spectral region (left image) to the 3 to 5 micron spectral region (right image) the bright, ice-rich region on Japetus turns dark and the dark region rich in organics turns bright".